The invention relates in general to data processing systems for real-time, multi-dimensional analysis and display. More particularly, the invention is directed to a real-time processing system that processes multi-dimensional acoustic signals.
Active and passive acoustics are used in a variety of systems, including systems that detect or monitor underwater objects, medical ultrasound systems, and in medical cardio-phonogram systems. The following discussion will principally refer to underwater active sonar systems, but as will be easily seen, the concepts are directly applicable to other imaging systems.
In the sonar world, various techniques are currently used to process active and passive acoustic data to detect and monitor surface vessels, submarines and other submerged objects, such as mines. Although acoustic data is inherently three-dimensional, having correlative values for distance (range), horizontal angle (bearing) and vertical angle (depth), known systems analyze the data in two dimensions only, and therefore must sacrifice data analysis in one of these dimensions. Prior art systems typically perform data calculation on the data at a particular depression/elevation (D/E) angle in a bearing by range format. Furthermore, in current systems, each bearing direction is processed separately. Prior art systems therefore can analyze data from only one direction, or bearing, and D/E angle at a single time, and cannot correlate data across several bearings while maintaining the bearing data separately.
Current sonar monitoring systems usually receive reverberation, noise and other unwanted echoes that obscure valid contacts, such as a submerged submarine. These systems may use advanced, "matched filter" processing to enhance detection and classification of sonar contacts. By transmitting a complex waveform, such as a linear frequency modulated (LFM) signal, it is possible to enhance the detection and classification of sonar contacts over that which could be attained through transmission of a ping or single, short pulse. Although the complex waveform may be much longer than a pulse, it is possible through pulse compression techniques (i.e. through the use of advanced correlation, or matched filter processing) to achieve high resolution range detection at lower signal-to-noise ratios. However, because of spatial and temporal variations in received acoustic energy, further processing is required to normalize the data for subsequent detection and display.
A typical low-frequency and mid-frequency (1-10 KHz) sonar monitoring system may consist of between 10 and 400 channels of data, each channel sampled at a rate in excess of 12,000 samples per second. These data are typically preprocessed, including automatic gain control, signal conditioning and frequency bandshifting. The result of this preprocessing generally results in a data rate reduced from thousands of samples per second (KHz) to a data rate under 300 samples per second per channel. Even at this lower data rate, a typical active sonar system may have to filter, detect, analyze and display well over 100,000 samples per second.
Similar active and passive acoustic data processing techniques are routinely used in the medical field. For example, sounds in the heart are monitored and analyzed using passive sonar monitoring data, resulting in cardio-phonograms.
Medical ultrasound diagnostic techniques use active sonar data to provide images of features in the body. High frequency sound waves (500 KHz to 25 MHz) are used to obtain information about the structure and functioning of organs in the body by producing images of blood flow and soft-tissue structures which are not readily visible through other medical modalities, such as x-ray, PET, MRI, etc. Images are created by transmitting ultrasound into the body and detecting ultrasound echoes off of tissue boundaries. Ultrasound transmissions may be in the form of pulsed energy at a high pulse repetition frequencies (PRFs). High frequencies and high PRFs enable finer resolution of internal structures. However high frequencies are more heavily attenuated within the body, resulting in weaker echoes from deep structures. Such undesirable effects may be somewhat ameliorated by increasing the power of the transmitted energy, but at the cost of increased reverberation, sidelobe leakage and other deleterious artifacts. Thus, the design and implementation of ultrasonic imaging systems generally involves trade-offs between range resolution, angular resolution and other, opposing physical effects. Consequently, most ultrasound systems require considerable attention from an operator or diagnostician in order to fine tune the systems to maximize the display of useful diagnostic information.
Ultrasound imaging systems may transmit pulsed energy along a number of different directions, or ultrasonic beams, and thereby receive diagnostic information as a function of both lateral direction across the body and axial distance into the body. This information may be displayed as two-dimensional, "b-scan" images. Such a two-dimensional presentation gives a planar view, or "slice" through the body and shows the location and relative orientation of many features and characteristics within the body. B-scan images may be updated as the ultrasonic transmissions are repeated at frame rates between 15 and 60 times a second. Therefore, computational load, resolution and overall performance are critical features in ultrasound systems. Furthermore, by tilting or moving the ultrasonic sensor across the body, a third dimension may be scanned and displayed over time, thereby providing three-dimensional information.
Alternatively, ultrasound returns may be presented in the form of "m-scan" images, where the ultrasound echoes along a particular beam direction are presented sequentially over time, with the two axes being axial distance versus time, which are updated up to 1,000 times a second. Thus, m-scan displays enable diagnosis of rapidly moving structures, such as heart valves. For some m-scan procedures, the sensor may remain at a single (lateral) direction, whereas for other procedures, the sensor may be tilted to sweep through the length of a heart or other internal organ.
Some ultrasound systems may combine both b-scan and m-scan images within the same display. This presentation of data may be helpful in locating and directing the orientation of the ultrasound beam for the m-scan display.
Other ultrasound systems may include doppler elements which may be used to monitor the flow direction and velocity of blood or other fluids within parts of the body. In some systems, a continuous wave (CW) tone is used to measure the average doppler signature along a particular beam direction within the body. Other systems which use pulsed wave (PW) doppler, may be used to obtain velocity information as a function of depth within the body.
Some ultrasound systems may operate in a duplex doppler mode, which combines both b-scan and doppler information in the same display. These systems present flow direction and speed along multiple directions and depths, presented as various colors superimposed upon b-scan images.
Other ultrasound imaging systems may simultaneously present multiple ultrasound information, including b-scan, m-scan and doppler image displays, along with other information, such as EKG signals and/or phonograms.
The present invention is designed to improve the ability to reduce interference in medical images caused by specular noise, gas, shadowing, reflections and "ghosting," in real-time. In a similar manner, the present invention is designed to improve the ability to reduce interference in sonar, including reverberation, clutter, multipath returns and specular noise.
The present invention is not limited to processing acoustic signals in ocean surveillance, medical imaging or medical monitoring systems. Digital data and images can be formed from a variety of other input data signals, including seismics, radar, lidar (laser), other electronic emissions, x-rays, including CAT scans, magnetic/RF emissions, including MRI and MRA, and visible light. Because such digital images require large amounts of computation and data storage, it is difficult to perform complex processing of the digital information on a real-time basis.
It is therefore an object of the present invention to provide a multi-dimensional acoustic data processing system that operates in "real-time."
It is a further object of the invention to provide a multi-dimensional acoustic data processing system that allows the suppression of certain features, interference, and noise, and the enhancement of other characteristics in order to "focus-in" on features or characteristics of interest.
It is also an object of this invention to enable the "data fusion," or intercorrelation, of multiple sets of data which describe different aspects of some physical entity or process.
Yet another object of the invention is to provide a multi-dimensional acoustic data processing system that compresses data for further processing and for transmission to a remote location and reconstitution of the received data to accurately represent the original image.
It is also an object of the invention to enhance and store acoustic data in a compressed form, for example as a movie replay of features moving within a three-dimensional, transparent data cube.